Gold and platinum are used as ornamental materials, raw materials of electrodes, catalysts or the like, palladium is used as catalysts, raw materials of hydrogen storing alloy or the like, iridium is used as raw materials of electrodes for electrolysis, spark plugs, semiconductor electrodes (flash memory, etc.) and melting pots or the like, and ruthenium and rhodium are used as raw materials of electrode, various kinds of ceramics and catalysts for purifying automobile exhaust gas, or the like which are industrially widely used.
To separates and recover these noble metals from raw materials containing the noble metals, there have been proposed various methods such as an electrolysis method, a chemical conversion method, an ion exchange method, a solvent extraction method, an adsorption method, and a combination method of them.
For example, in separating and recovering gold from raw ore, there have been known a method of solving raw ore to separate gold-containing fractions, treating them into gold-salt-containing aqueous solution by hydrochloric acid and chlorine or aqua regia, and electrolyzing the gold-salt-containing solution, thereby separating and recovering gold (see Patent Document 1 as mentioned below), a method of treating gold-salt-containing solution by ion exchange resin (see Patent Document 2), a method of solvent extraction with dibutyl carbitol (see Patent Document 3), a method for recovery by solvent extraction using 4-methyl-2-pentanon and adsorption to chelate resin (see Patent Document 4), and a method for recovery by adsorption on peat (Patent Document 5).
In these methods, since gold is recovered as gold salt, finally, it is necessary to convert gold salt into gold by reduction treatment.
As a method for separating and recovering each noble metal from raw materials containing a plural kinds of noble metals, there have been known method as follows: a method of passing a chloride solution containing at least two noble metals through at least one chromatographic column containing a solid adsorbent having a Kd above 1, which adsorbs the noble metals on the adsorbent, and subsequently eluting the noble metals by a halide salt solution, to obtain thereby separate fractions, each fraction containing only one single noble metal and coming out in the order: Ru, Rh, Pd, Pt, Ir and Cs (see Patent Document 6); an interseparation method of noble metals comprising: passing a noble-metal-containing halide feed solution through a chromatograph medium and adsorbing noble metals on the medium; and eluting the noble metals using an eluent to obtain separate fractions, each fraction containing at least one noble metal so that Ir and Ru ions are separated in an trivalent oxidation state (see Patent Document 7); a method for the interseparation of iridium from an admixture of noble metals containing iridium and other noble metals, comprising: passing an acidic solution containing chlorocomplexes of iridium and other noble metals through at least one chromatography column containing a solid absorbent; eluting one or more fractions containing one or more noble metals; ensuring the iridium is present on the column in a tetravalent oxidation state; and reducing the iridium on the column from a tetravalent oxidation state to a trivalent oxidation state and separating an iridium (III) chlorocomplex from chlorocomplexes of other noble metals; (see Patent Document 8); a method of inter-separating platinum-group metals comprising; (a) adjusting the acidity of the feedstock solution to be in the range of 5.5 to 6.5 M HCl, (b) adjusting the redox potential of the feedstock solution to at least approximately 500 mV, (c) passing the acidity- and redox-adjusted solution through a chromatographic medium causing the base metals, other impurity elements and platinum-group metals to interact with the chromatographic medium, and (d) eluting at least platinum and palladium in separate fractions from the medium using an eluent (see Patent Document 9); and a method of interseparating noble metals from a halide solution thereof, the method comprising: passing the solution through a glycol metacrylate chromatographic medium, adsorbing the noble metals onto the medium, and eluting each adsorbed noble metal with an acidic solution to obtain separate fractions (see Patent Document 10).
However, in all of these methods, it is necessary to use special adsorbents and eluents, thereby raising costs. In addition, the separation operation is complicated and separation efficiency is low. Therefore, these methods are not satisfactory as the industrial method for separation of noble metals.
Accordingly, in this field, a method for separation and recovery of noble metals has been demanded, which uses easily available adsorbents and eluents and makes it possible to isolate noble metals by easy operation, and is thereby industrially satisfactorily usable.
Cellulose is an easily available and low cost adsorbent, and there were reported several examples of separating noble metals using cellulose. For example, as a method of separating platinum using a cellulose column, there was reported a method of obtaining noble metal chlorides, the method comprising: passing an admixture of conc. hydrochloric solution of platinum, palladium, rhodium and iridium through the cellulose column, developing 4-methyl-2-pentanon as a mobile phase, firstly eluting platinum and iridium, subsequently eluting palladium, consequently eluting rhodium, and eliminating 4-methyl-2-pentanon from these eluates to obtain separate noble metal chlorides (Non-Patent Documents 1 and 2).
However, also in this case, it is necessary to use a special eluent, the operation is complicated, and the separation efficiency is low. Therefore, the method is thoroughly inappropriate to industrial application.
Thus, the present inventors had been carried out various researches on a method for individually separating and recovering noble metals from raw materials containing a plurality of noble metals and base metals by easy operation, using a cellulose column and using an easily available solvent as an eluent. As a result, the present inventors proposed a method for separating and recovering noble metals, the method comprising: dissolving raw materials with a hydrochloric acid to extract a plurality of noble metals and base metals as chloride solutions, passing the hydrochloric acid solution containing these metals through a cellulose column to adsorb noble metals thereon, subsequently eluting rhodium, palladium and the like from the column by using a mixed solution of hydrochloric acid and 2-propanone as a first eluent, and then eluting the other noble metals such as gold, platinum, iridium and ruthenium by using a mixed solution of hydrochloric acid and 1-butanol as a second eluent (Patent Document 11).
However, in this method, since the noble metals adsorbed on the single cellulose column are eluted by two kinds of eluents with the lapse of time, a long time is necessary from the time when the first group noble metals are completely eluted by the first eluent to the time when the elution is carried out by the second eluent. Accordingly, it is difficult to avoid that the whole operation time becomes long. In addition, in the case of reusing the cellulose column after all noble metals are eluted, the cellulose is alternately exposed to two different kinds of eluents, thereby significantly decreasing mechanical strength thereof. Moreover, adsorption capability of cellulose with respect to noble metals deteriorates, and thus the number of times of repeated uses decreases.
Patent Document 1: U.S. Pat. No. 4,229,270B
Patent Document 2: U.S. Pat. No. 4,543,169B
Patent Document 3: U.S. Pat. No. 4,390,366B
Patent Document 4: U.S. Pat. No. 4,762,556B
Patent Document 5: U.S. Pat. No. 4,936,910B
Patent Document 6: U.S. Pat. No. 4,885,143B
Patent Document 7: JP 9-133670A
Patent Document 8: JP 2001-98335A
Patent Document 9: JP 2001-516808A
Patent Document 10: JP 2002-303614A
Patent Document 11: JP 2006-193763A
Non-Patent Document 1: “Anal. Chim. Acta”, 1958, pp. 129-131
Non-Patent Document 2: S. I. Ginzburg et al., “Analytical Chemistry of Platinum Metals”, N.Y. Wiley & Sons, 1975, pp. 466-479.